Python: Emit tool call events in GitHubCopilotAgent streaming (microsoft#4711)

* Emit tool call events in GitHubCopilotAgent streaming

_stream_updates now yields FunctionCallContent for TOOL_EXECUTION_START
and FunctionResultContent for TOOL_EXECUTION_COMPLETE events from the
Copilot SDK session. This enables DevUI and other consumers to display
tool calls during streaming agent execution. Previously only ASSISTANT_MESSAGE_DELTA, SESSION_IDLE, and SESSION_ERROR
were handled — tool execution events were silently dropped.

Signed-off-by: James Sturtevant <jsturtevant@gmail.com>

* Add some tests

Signed-off-by: James Sturtevant <jsturtevant@gmail.com>

* Respond to feedback

Signed-off-by: James Sturtevant <jsturtevant@gmail.com>

* Fix TOOL_EXECUTION_COMPLETE to use correct SDK types

- Read result text from session_events.Result.content (not ToolResult.text_result_for_llm)
- Read failure state from event.data.success/error (not result_obj.result_type/error)
- Handle ErrorClass.message and plain string errors
- Update tests to use session_events.Result and ErrorClass
- Add tests for string errors, success-with-error, and COMPLETE missing fields

Signed-off-by: James Sturtevant <jsturtevant@gmail.com>

---------

Signed-off-by: James Sturtevant <jsturtevant@gmail.com>

Author: jsturtevant

python/packages/github_copilot/agent_framework_github_copilot/_agent.py

@@ -458,6 +458,43 @@ def event_handler(event: SessionEvent) -> None:
                         raw_representation=event,
                     )
                     queue.put_nowait(update)
+            elif event.type == SessionEventType.TOOL_EXECUTION_START:
+                tool_call_id = getattr(event.data, "tool_call_id", None) or ""
+                tool_name = getattr(event.data, "tool_name", None) or ""
+                arguments = getattr(event.data, "arguments", None)
+                fc = Content.from_function_call(
+                    call_id=tool_call_id,
+                    name=tool_name,
+                    arguments=arguments,
+                    raw_representation=event.data,
+                )
+                update = AgentResponseUpdate(
+                    role="assistant",
+                    contents=[fc],
+                    raw_representation=event,
+                )
+                queue.put_nowait(update)
+            elif event.type == SessionEventType.TOOL_EXECUTION_COMPLETE:
+                tool_call_id = getattr(event.data, "tool_call_id", None) or ""
+                result_obj = getattr(event.data, "result", None)
+                result_text = getattr(result_obj, "content", "") if result_obj else ""
+                success = getattr(event.data, "success", None)
+                error_val = getattr(event.data, "error", None)
+                exception = None
+                if success is False and error_val is not None:
+                    exception = error_val.message if hasattr(error_val, "message") else str(error_val)
+                fr = Content.from_function_result(
+                    call_id=tool_call_id,
+                    result=result_text or "",
+                    exception=exception,
+                    raw_representation=event.data,
+                )
+                update = AgentResponseUpdate(
+                    role="tool",
+                    contents=[fr],
+                    raw_representation=event,
+                )
+                queue.put_nowait(update)
             elif event.type == SessionEventType.SESSION_IDLE:
                 queue.put_nowait(None)
             elif event.type == SessionEventType.SESSION_ERROR: